Piezoactuators include electrode layers that engage each other like combs. The electrode layers in each comb are electrically connected via contact layers that are arranged at the edge of the stack, and are produced from a silver firing paste. In a center region of the stack, where the electrode layers that belong to different combs overlap. the actuator expands when an electrical voltage is applied. No such expansion takes place in the edge regions of the stack. This results in tensile stresses in the inactive edge regions of the stack.
The tensile stress resistance of ceramic, which is used as a piezoelectric material, is low. Cracks that occur at a border between the center region and the edge region can spread on a surface of the ceramic, thereby endangering the operability of the component. This is because electrode layers in the actuator must be electrically connected to one another, i.e., in contact, to supply voltage at side surfaces of the actuator. An interruption in this electrical connection between electrode layers endangers the voltage supply to the electrode layers. This is because currents can cause resistive heating at a damaged contact location, which leads to thermal destruction of an existing residual conductive connection.
To prevent formation of cracks in the edge region of the actuator, a piezoactuator can be moderately pressure-stressed. Such moderate stress can be provided by clamping the stack into a tube string. The tube spring presses the base surface and the cover surface, respectively, of the actuator against one another at a uni-axial pressure of approximately 850 N.
Moreover, to prevent a failure of electrode layers during interruption of the contact layers arranged at the edge of the stack, numerous individual wires are soldered onto the actuator at regular intervals.
Clamping the actuator into a tube spring and applying of a large number of solder sites onto the contacting layer are complicated processes and are costly.